A solid electrolytic capacitor element is constituted of an anode body including a conductive material such as a sintered body of a valve action metal powder, a dielectric layer of a metal oxide formed on the surface by subjecting the surface layer of the anode body to electrolytic oxidation in an aqueous solution of an electrolyte such as phosphoric acid, and a solid cathode layer (semiconductor layer) composed of a conductive polymer formed thereon by electrolytic polymerization or the like.
For example, in Patent Document 1, an electrolytic capacitor using tantalum, niobium, titanium, aluminum, hafnium, zirconium or the like as a valve action metal has been described. For example, in Patent Document 2, an electrolytic capacitor using niobium as a valve action metal has been described.
In addition to the valve action metals listed above, for example, in Patent Document 3, an electrolytic capacitor using a sintered body of tungsten powder has been described. The electrolytic capacitor using a sintered body of tungsten powder is capable of obtaining a large capacitance as compared with the electrolytic capacitor using a sintered body of another valve action metal. On the other hand, the electrolytic capacitor using a sintered body of tungsten powder has been studied, since there are problems such as cracking of the coating film in the chemical conversion step and a large leakage current.